1. Field of the Invention
This invention relates generally to porous dielectric films useful in the semiconductor industry, and more particularly to processes for making such films by chemical vapor deposition using chemical precursors that contain carbon and oxygen.
2. Description of the Related Art
As the dimensions of microelectronic devices become smaller, the importance of the physical properties of the materials used in their manufacture becomes more important. This is particularly true of the dielectric materials that are used to insulate metal lines and vias from one another because of the contributions to capacitance that these materials make. Silicon dioxide has been employed within the industry as a dielectric material for the manufacture of devices for nearly four decades, but may become less suitable in the future because of its relatively high dielectric constant (kxcx9c4.1).
The dielectric constant of silicon dioxide can be reduced by introducing porosity to produce a material known as porous silica. Wet methods for making porous silica typically involve coating a substrate with a solution that contains a solvent and a silica precursor, then evaporating the solvent under controlled conditions to form the porous silica. See, e.g., L. Hrubesh, Mat. Res. Soc. Symp. Proc. Vol. 381, p. 267-272 (1995); U.S. Pat. Nos. 5,470,802; 5,569,058; 5,847,443; 6,140,252; 6,208,014; and 6,261,357. U.S. Pat. No. 6,261,469 discloses a method for assembling small silica spheres into a lattice structure by a sedimentation process from a colloidal suspension of the silica spheres. U.S. Pat. No. 6,022,812 discloses depositing an alkoxysilane composition onto a substrate, exposing the deposited composition to water vapor and either an acid or a base vapor, and drying the composition to produce porous silica. PCT Patent Application WO 01/78127 discloses the use of a high density plasma to densify porous silica in order to make it more compatible for adhesion to a cap layer.
U.S. Pat. No. 6,171,945 discloses a method for depositing a porous silicon oxide layer using chemical vapor deposition. The method involves condensing a peroxide compound on the surface of a substrate and contacting the deposited peroxide compound with a reactive compound or mixture containing hydrogenated silicon. U.S. Pat. No. 6,238,751 discloses depositing an organic-group-containing silica precursor on a substrate in a chemical vapor deposition reactor, then removing the organic groups by heating or exposure to a plasma to produce a low density silica film.
There remains a need for porous silica materials having better properties more suitable for use in microelectronics manufacturing, and for processes for producing such materials that can be readily integrated into fabrication process flows.
A preferred embodiment provides a method for making a porous silica film, comprising depositing a Sixe2x80x94Oxe2x80x94C film having a dielectric constant k1 by chemical vapor deposition using a carbon oxygen compound and a silicon source, the carbon oxygen compound being free of silicon atoms; and heating the Sixe2x80x94Oxe2x80x94C film to produce a porous silica film having a dielectric constant k2, wherein k1 greater than k2.
Another preferred embodiment provides a method for making a porous silica film, comprising depositing a graded Sixe2x80x94Oxe2x80x94C film having an overall dielectric constant k1 by chemical vapor deposition using a feed gas, wherein the feed gas comprises an amount of a carbon oxygen compound that is varied over the course of the depositing; and heating the Sixe2x80x94Oxe2x80x94C film to produce a graded porous silica film having an overall dielectric constant k2; wherein k1 greater than k2 and wherein the graded porous silica film has a degree of porosity that varies significantly through the film.
Another preferred embodiment provides a method for making a porous silica film, comprising depositing a Sixe2x80x94Oxe2x80x94C film having a dielectric constant k1 by pulsed plasma-enhanced chemical vapor deposition using a carbon oxygen compound and a silicon source; and heating the Sixe2x80x94Oxe2x80x94C film to produce a porous silica film having a dielectric constant k2, wherein k1 greater than k2.
These and other embodiments are described in greater detail below.